1. Field of the Invention
This invention relates to a drill rod for rotary drilling apparatus and more particularly to a drill rod assembly formed by a plurality of individual releasably engageable drill rod members that are restrained from separation from one another upon removal of the drill rod assembly from the drilled bore hole.
2. Description of the Prior Art
In underground mining operations, a mine roof is conventionally supported by roof bolts that include an expandable shell positioned in a bore hole drilled in the mine roof and a bearing plate positioned on the roof bolt in contact with the mine roof at the emergent end of the bore hole. Rotating the bolt having an expansion shell positioned on the opposite end thereof expands the shell to engage the rock wall of the bore hole. The bolt is tensioned with the resultant effect of compressing the rock strata to reinforce the strata and thereby prevent roof falls. It is also known to support a rock formation by adhesively bonding an elongated bolt in a bore hole drilled in a mine roof. The bolt is adhesively bonded in position by a thermosetting resin having thixotropic properties.
Vertical bores or bolt holes are drilled in the mine roof by a roof drill that is mounted on the end of a boom of a mobile drilling machine. The boom is connected to the mobile machine so that, as the boom is raised, the roof drill moves in a vertical linear path to drill a substantially vertical bore hole in the mine roof. In many underground mining operations, because of the low seam heights, the roof bolts require a bore of a length greater than the height of the mine roof, i.e. the clearance between the mine roof and floor. Therefore, a drill steel or drill rod is formed by a plurality of interconnected rod sections. The rod sections are progressively added to the drill rod as the bore hole is being developed in the mine roof.
Once the bore hole has been drilled to the required depth in a mine roof, the drill rod assembly or drill steel must be removed from the bore hole for insertion of the roof bolt. In most cases, particularly when drilling in relatively hard rock strata, it is extremely difficult to maintain the drill steel aligned with a vertical axis for drilling a vertical bore hole. Most commonly, the drill steel will penetrate the hard material and be deflected from a precise vertical position. It is also the conventional practice for the operator to steady the drill steel with his hand to start the bore hole. The operator continues to hold the drill steel as it advances into the mine roof to maintain the drill steel in a vertical axis for drilling a bore hole in a straight line. This is a dangerous practice and subjects the drill operator to a substantial risk of injury.
When the drill steel is deflected from a vertical position, it rubs against the side wall of the bore hole. Consequently, as the drill steel is retrieved after the bore hole has been drilled to the desired depth, the friction generated between the drill steel and the wall of the bore hole obstructs withdrawal of the drill steel from the bore hole. For a drill steel formed by a plurality of slidably interconnected male and female sections, the frictional engagement of the sections with the bore hole wall overcomes the engagement of the interconnected sections resulting in separation of one or more of the sections.
One known solution to preventing loss of drill rod sections in a bore hole upon retrieval of the drill rod assembly is the use of pins to connect the adjacent sections. Couplings are also used to connect adjacent drill rod sections, as disclosed in U.S. Pat. No. 3,519,091. A conventional coupling includes a socket end portion and a rod end portion where the socket end portion has a rectangular or hexagonal profile and the shank end portion has a corresponding profile. The shank end portion of a drill rod section also having a hexagonal or rectangular profile is inserted within the receiving socket of the coupling. The drill rod shank end portion may also be provided with a split ring that is compressed when forced into the coupling socket to frictionally engage the shank in the socket. It is also known to utilize a detent mechanism to hold a hexagonal drill rod shank end portion within a mating coupling socket.
U.S. Pat. No. 4,226,290 discloses the connection of adjacent drill rod sections by inserting a male shank within a female socket and aligning a groove in the male shank with a hole in the female socket. A locking wire is positioned in the aligned hole and groove so as to prevent the separation of the connected drill rod sections.
The use of pins and wires to connect sections of a drill rod assembly is considered to be inconvenient in the working environment of an underground mine. Due to the confined working area of an underground mine, the maneuverability of the mine drill is limited, making it difficult to connect drill rod sections by pins and wires. Also, these elements are easily lost, and an adequate inventory must be maintained at the work site. The same applies to couplings for connecting adjacent drill rod sections. Furthermore, the use of any connecting element to join adjacent drill rod sections increases the time to complete the drilling of a bore hole and thus the time the drill operator is exposed to unsupported mine roof.
As disclosed in U.S. Pat. No. 4,226,290, it is known to position various drill rod components in a predetermined order in the drilling of a bore hole. For example, the drill bit is initially attached to the upper end of a starter bar which is positioned in the drill head chuck to initiate drilling of the bore hole. Once the bore hole has been started, the starter bar and drill bit are removed by lowering the drill head and a driver steel component is inserted within the chuck of the drill head. A finisher component, which holds the drill bit, is connected to the driver steel component, and the drilling is continued. As the bore hole is developed, middle extension components are inserted between the driver steel component and the finisher component to achieve the requisite bore height. With this arrangement, a number of distinct drill steel components must be connected in a preselected order to one another by interconnected pins and wires, couplings or the like to form a complete drill rod. This method requires a substantial inventory of distinct components that are not interchangeable.
Therefore, there is need in rotary drilling apparatus for a drill rod formed by a plurality of drill rod sections connected in a manner that resists separation of the sections upon retrieval of the drill rod from the drilled bore hole and facilitates efficient assembly and disassembly of the respective sections. While the known drill rod assemblies include connected components to resist separation of the drill rod sections from one another during retrieval of the drill rod, the known drill rod assemblies require the use of a number of different components which increase the inventory demand and the time for drilling a bore hole. This reduces the mining production by slowing the drilling operation and increases the occupational hazards involved in mine roof drilling.